1. Field of the Invention
The present invention relates to a membrane electrode assembly structure for a fuel cell and a method for fabricating the same, more particularly, relates to improving the toughness and mechanical strength of an anode substrate to reduce the thickness of the substrate, thereby solving the problem of cracking during packaging and testing, increasing the output power density of the fuel cell to provide a stable electric power output in a longer duration.
2. Description of Related Art
A solid oxide fuel cell membrane electrode assembly (SOFC-MEA) is an energy conversion device that converts fuel to electric energy by electrochemical reaction. The traditional solid oxide fuel cell with the electrolyte supported cell (ESC) operates in a temperature range between 800 and 1000° C., and the thickness of the electrolyte layer is about 150-300 μm. Because the thickness of the electrolyte is thick and the overall bulk impedance is large that explains the ESC SOFC needs to operate in a higher temperature.
The thickness of YSZ electrolyte layer with NiO-YSZ anode supported cell (ASC) is below 10 μm, so the operating temperature can be reduced to in a range between 650 and 800° C. Before the cell is to be electrically tested in stack, the cell is packaged and it is subjected to pressure during the electrical measurement. Therefore, the mechanical strength of the cell becomes one of the important factors to be considered in the process.
The fabrication process of the traditional anode-supported SOFC-MEA is based on the tape casting technology to produce the anode green tape, and then the thickness and geometrical structure of the green substrate is adjusted by the laminating technique, followed by using a thin film ceramic process and a high temperature densification sintering process to produce a half-cell substrate including an anode supported layer and an electrolyte layer, and finally a cathode layer is built on the half-cell substrate by a screen printing technique to complete the production.
However, the main drawbacks of the conventional process described above are the poor stability and durability during reduction-oxidation cycling and thermal cycling test. In considering the basic requirements of the cathode and anode porosity in order to facilitate gas-solid reaction mechanism under the basic conditions, it is unavoidable to sacrifice mechanical strength, resulting in the subsequent cell stack packaging prone to failure situations, the mentioned above shortcomings also hinder the application and development of the SOFC.
In view of the foregoing drawbacks of the conventional fuel cell membrane electrode assembly, the inventors of the present invention have studied the drawbacks and sought for solutions.